"The extensive pipeline system that moves oil, gas and waste throughout BP's operations in Alaska is plagued by severe corrosion, according to an internal maintenance report generated four weeks ago.

The document, obtained by ProPublica, shows that as of Oct. 1, 2010 at least 148 BP pipelines on Alaska's North Slope received an "F-rank" from the company. According to BP oilworkers, that means inspections have determined that more than 80 percent of the pipe wall is corroded and could rupture. Most of those lines carry toxic or flammable substances. Many of the metal walls of the F-ranked pipes are worn to within a few thousandths of an inch of bursting, according to the document, risking an explosion or spills."